无连接模式：可以在没有打开连接时在内存中操作数据，DataAdapter通过管理连接为无连接模式提供服务，当要从数据库中查询数据时，DataAdapter打开一个连接，填充指定的DataSet,等数据读取完马上自动关闭连接，然后可以对数据做修改，再次使用DataAdapter打开连接，持久化修改(无论是更新，删除或是更新)，最后自动关闭连接，使用无连接模式的情况是有一些独立数据，它们不会发生改变或者很少改变，因为在将填充DataSet和更新数据这段时间内数据库中的实际数据也许会发生改变，如果需要将数据立即持久化到数据库请使用连接模式
读取数据到DataSet:无连接意味着一个连接建立了一个与数据库的会话，请求的数据读入到DataSet中，然后通过断开数据库的连接关闭会话，这时会话因为与数据库的断开而关闭，DataSet成为一个无连接的数据库
/// <summary>
/// 查询学生信息
/// </summary>
/// <returns>返回填充了学生表的DataSet</returns>
public DataSet GetUserInfor()
{
string str = "Data Source=.;Initial Catalog=Student;Integrated Security=True";
var conn = new SqlConnection(str);
DataSet ds = new DataSet();
var sda = new SqlDataAdapter("SELECT * FROM Student",conn);
sda.Fill(ds, "student");//调用fill方法时，SqlDataAdapter会自动打开连接，读取数据然后关闭连接
foreach (DataRow dr in ds.Tables["student"].Rows)
{
Console.WriteLine(dr["name"]);
}
return ds;
}
将DataSet的修改保存到数据库
插入数据
/// <summary>
/// 插入学生信息，并返回插入后的DataSet
/// </summary>
/// <param name="stu">学生实体类</param>
public DataSet InsertStudnt(Student stu)
{
DataSet ds = GetUserInfor();
string str = "Data Source=.;Initial Catalog=Student;Integrated Security=True";
string sql = "INSERT INTO student VALUES (@name,@age)";
var conn = new SqlConnection(str);
var cmd = new SqlCommand(sql,conn);
var sda = new SqlDataAdapter();
SqlParameter sqlParam1 = new SqlParameter()
{
ParameterName = "@name",
SourceColumn = "name"
};
SqlParameter sqlParam2 = new SqlParameter()
{
ParameterName = "@age",
SourceColumn = "age"
};
SqlParameter[] sqlParamArray = new SqlParameter[] {sqlParam1,sqlParam2 };
cmd.Parameters.AddRange(sqlParamArray);
sda.InsertCommand = cmd;
DataRow dr = ds.Tables["student"].NewRow();
dr["name"] = stu.name;
dr["age"] = stu.age;
ds.Tables["student"].Rows.Add(dr);
sda.Update(ds,"student");
return ds;
}
更新数据
/// <summary>
/// 根据ID更新姓名和年龄
/// </summary>
/// <param name="name">姓名</param>
/// <param name="age">年龄</param>
/// <param name="id">学生ID</param>
/// <returns>返回更新后的DataSet</returns>
public DataSet UpdateStudent(Student stu,int id)
{
DataSet ds = GetUserInfor();
string str = "Data Source=.;Initial Catalog=Student;Integrated Security=True";
string sql = "UPDATE student SET name=@name,age=@age WHERE id=@id";
var conn = new SqlConnection(str);
var cmd = new SqlCommand(sql, conn);
var sda = new SqlDataAdapter();
SqlParameter param1 = new SqlParameter()
{
ParameterName="@name",SourceColumn="name"
};
SqlParameter param2 = new SqlParameter()
{
ParameterName = "@age",
SourceColumn = "age",
SqlDbType=SqlDbType.Int
};
SqlParameter param3 = new SqlParameter()
{
ParameterName = "@id",
SourceColumn = "id"
};
SqlParameter[] param = new SqlParameter[] {param1,param2,param3 };
cmd.Parameters.AddRange(param);
sda.UpdateCommand = cmd;
DataTable dt = ds.Tables["student"];
foreach (DataRow dr in dt.Rows)
{
int oldID=Convert.ToInt32(dr["id"]);
if (oldID == id)
{
dr["name"] = stu.name;
dr["age"] = stu.age;
}
}
sda.Update(ds,"student");
return ds;
}
删除数据
/// <summary>
/// 根据ID删除一个学生
/// </summary>
/// <param name="id">返回更新后的DataSet</param>
public DataSet DeleteStudent(int id)
{
DataSet ds = GetUserInfor();
string str = "Data Source=.;Initial Catalog=Student;Integrated Security=True";
string sql = "DELETE FROM student WHERE id=@id";
var conn = new SqlConnection(str);
var cmd = new SqlCommand(sql, conn);
var sda = new SqlDataAdapter();
SqlParameter param = new SqlParameter()
{
ParameterName="@id",SourceColumn="id",SqlDbType=SqlDbType.Int
};
cmd.Parameters.Add(param);
sda.DeleteCommand = cmd;
DataTable dt=ds.Tables["student"];
foreach (DataRow dr in dt.Rows)
{
int oldId = Convert.ToInt32(dr["id"]);
if (oldId == id)
dr.Delete();
}
sda.Update(ds,"student");
return ds;
}
